Process and apparatus for enhancing boron removal from water

ABSTRACT

A process and apparatus for enhanced boron removal from water. The process includes the steps of reacting potassium carbonate or ammonium carbonate with calcium borate in a stream of feed water to form a stream having calcium carbonate and potassium borate salt or ammonium borate salt. The stream having calcium carbonate and potassium borate or ammonium borate is introduced to an ion exchange vessel containing resin having methylglucamine in salt form with potassium carbonate or sodium carbonate to form borate and potassium sulfate or sodium sulfate. The resin in the ion exchange vessel is periodically regenerated.

CROSS REFERENCE

This application is a continuation of U.S. patent application Ser. No.15/618,204, filed Jun. 9, 2017, which claims priority to and the benefitof U.S. Provisional Patent Application Ser. No. 62/392,710, filed Jun.9, 2016, each of which is incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention is directed to an enhanced method or process toremove boron from water utilizing an unpressurized, open ion exchangeresin vessel. In addition, the present invention provides a process ormethod for regeneration of the resin utilized in the boron removalprocess and provides an ambient temperature process and apparatus forconcentration of the regeneration output.

Description of the Related Art

Agriculture, such as orchards and vineyards, requires vast amounts ofwater for irrigation. Irrigation demand peaks at various times, such asin mid-summer. While trace amounts of boron are known to promote plantgrowth, excessive boron levels in water are known to be toxic to plants.Some normal irrigation water sources, such as well water, contain highlevels of boron. In addition, excessive boron in potable water isundesirable. Indeed, some jurisdictions or areas are considering boronlimits in drinking water.

Desalinated water from oil and gas well production and from seawaterdesalination reverse osmosis is especially high in boron content. It isdesirable to desalinate oil well production water in order to minimizedeep well injection of this water. Therefore, it is also desirable toremove boron from the water both quickly and economically.

Existing processes and procedures for boron removal from water areconsidered prohibitively expensive for many applications. Known boronremoval resin is expensive, so maximizing boron loading capacity andflow through ion exchange resin beds is important.

Various known prior art approaches to boron removal from water are asfollows:

Reverse Osmosis

In the case of reverse osmosis, the high volume of reject (retentate)water is expensive to transport and dispose of in deep injection wellsor other means. Reverse osmosis is nonselective, so all the salt isremoved. This limits the yield of product water. The pH must beincreased before reverse osmosis to remove sufficient amounts of boronfrom the water, which increases the salt level of reject water evenmore. The product (permeate) water is too alkaline for many uses.

Therefore, acid must be added to restore a proper pH for irrigation andother uses.

Ion Exchange

Boron selective ion exchange resin is expensive and has relatively lowloading capacity. Loading capacity can be compromised by the presence ofvarious chemicals in the source water. In addition, the standardregeneration process is a two-step process which requires regenerationwith acid followed by regeneration with caustic. The two-step processdoubles the regeneration time. Since many water sources containcarbonates, the standard downward flow acid regeneration compromisesboron removal, due to CO2 gas release into the resin bed duringregeneration. This limits acid access to the resin. The resultingregeneration waste is a dilute mixture of sodium chloride, boric acidand sodium borate. This mixture does not have a commercial value and isconsidered a hazardous liquid waste, which is expensive to transport anddispose of. The volume of regeneration waste is too expensive toconcentrate by conventional means, such as membranes or common energyintensive evaporators.

Pressurized Resin Vessels

Since the resin is expensive it is desirable to have large diametervessels with minimal resin depth to maximize resin loading capacity,while minimizing pressure drop across the resin bed during service mode.However, large diameter pressure vessels are expensive, while multiplesmall vessels are complex to operate and require several valves.

Evaporation

The evaporation of water with high salt content is an energy intensiveprocess. The use of solar ponds is an energy free method; however, theaverage evaporation rate is quite slow at 0.006 to 0.009 inches perhour. A 10 ft. diameter pond would have an evaporation rate of 0.3 to0.5 gallons per hour.

Multiple effect evaporators are more energy efficient to operate butrequire expensive equipment. Similarly, vapor recompression requiresexpensive equipment and requires significant mechanical energy. Neitherof these methods performs well when evaporating liquids to solids.

There still remains a need for a cost efficient high-volume process toremove boron from water.

Accordingly, it is a principal object and purpose of the presentinvention to provide an enhanced process and apparatus for boron removalfrom water.

It is a further object and purpose of the present invention toregenerate boron removal resin.

It is a further object and purpose of the present invention to provide aprocess and apparatus to concentrate boron in a liquid stream.

SUMMARY OF THE INVENTION

The present invention is directed to a process and an apparatus forenhanced boron removal from feed water. In one preferred embodiment, theprocess includes the steps of reacting potassium carbonate or ammoniumcarbonate with calcium borate in a stream of feed water in order to forma stream having calcium carbonate and potassium borate salt or ammoniumborate salt. The stream having the calcium carbonate and potassiumborate or ammonium borate is introduced into an ion exchange vesselthrough a diffuser screen. The vessel contains a macroporous polystyreneresin having methylglucamine in salt form and potassium carbonate orsodium carbonate in order to form borate and potassium sulfate or sodiumsulfate.

The resin in the ion exchange vessel is periodically regenerated whilein the vessel. A level of liquid is maintained in the ion exchangevessel having resin. Acid is pumped into the liquid while recirculatingto a base of the vessel in order to percolate the acid through theresin. Carbon dioxide bubbles which are formed thereby are removed froma top of the vessel. The liquid having borate is thereafter removed to aboron tank. Fresh water is introduced to the ion exchange vessel and atleast a portion of the liquid is directed to a recycle tank.

The borate in the liquid stream which has been delivered to the boronstorage tank may be concentrated or evaporated. The liquid containingborate is pumped from the boron storage tank to a cooling tower. Theliquid is thereafter sprayed through a nozzle or nozzles from above thecooling tower. Ambient air is drawn upward through the cooling tower byaction of a fan. Concentrated liquid falls by gravity back into theboron tank. The higher density liquid falls toward the base of the tankwhile the lower density material remains or migrates to the top of thetank. Borate is concentrated along with borate crystals at a base of thetank.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a sectional view of a prior art ion exchange vessel;

FIG. 2 illustrates a sectional view of an ion exchange vessel for use inan apparatus and process for enhancing boron removal of the presentinvention;

FIG. 3 illustrates a simplified schematic diagram of the apparatus ofthe present invention;

FIG. 4 illustrates a cut away diagram of a portion of the ion exchangevessel of the present invention; and

FIG. 5 illustrates a sectional view of an evaporator of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments discussed herein are merely illustrative of specificmanners in which to make and use the invention and are not to beinterpreted as limiting the scope.

While the invention has been described with a certain degree ofparticularity, it is to be noted that many modifications may be made inthe details of the invention's construction and the arrangement of itscomponents without departing from the scope of this disclosure. It isunderstood that the invention is not limited to the embodiments setforth herein for purposes of exemplification.

Agricultural irrigation requires very large water flows. In order toremove chemicals such as boron, this translates into many small ionexchange pressure vessels, since large diameter pressure vessels areexpensive. The management and control of many small vessels requires anextensive network of valves. At high flow rates, the pressure dropacross prior art ion exchange vessels can exceed 10 PSI, which makes anopen ion exchange vessel appear impracticable

The large pressure drop is mostly due to the large increase in watervelocity past the resin as it approaches the collector at the bottom ofthe ion exchange vessel. For example, see Prior Art in FIG. 1. The flowrate across the resin bed is 6 gpm/sqft, while the flow across the resinnear the collector is 60 gpm/sqft. Ninety-percent of the pressure dropoccurs across the collector. Due to the high cost of pressure vessels,greater resin depths are favored, which also contributes to the highpressure drop across the resin vessel. See Prior Art in FIG. 1.

FIG. 2 illustrates a sectional view of an ion exchange vessel 12 for usein the process and apparatus of the present invention. FIG. 3illustrates a simplified schematic diagram of the apparatus 10 of thepresent invention. The ion exchange vessel 12 may include asubstantially closed container with an open top which is maintained andoperated at both ambient temperature and ambient pressure.

Feed water, such as from a subterranean well, moved by a pump is broughtto the ion exchange vessel 12, as shown by arrow 14. The feed water maycontain boron, such as in the form of calcium borate. The feed water isdelivered to a screen, such as a diffuser 18 having slots therein. Thediffuser 18 promotes uniform flow across the resin bed (to be described)and minimizes resin agitation in the service mode. The level of water inthe service mode is shown by water line 20.

A blend valve 22 permits blending of treated water (to be described)with incoming feed stream water to allow any concentration level ofboron between the subterranean well water boron level and the outputboron level.

The ion exchange vessel 12 may include a layer of gravel 24 at the baseof the vessel with a layer of sand 26 thereon.

Well screen pipes 30 are placed near the bottom of the vessel 12 withsubstantially uniform spacing such that the area of the well screen pipeis similar to the surface area of the bottom of the resin bed. Wellscreen spacing approximately equal to the perimeter of the well screenpipe may be preferred. The well screens 30 are connected to manifolds32. The well screen manifolds 32 are connected to a manifold pipe 34above the level of the resin bed.

The manifold pipe 34 is connected to an irrigation pump 76 havingnegative pressure, such as a centrifugal pump, to draw or suck the waterthrough the resin in the resin bed and thereafter transport the outgoingwater, such as to an irrigation system. The level of water in the resinbed is maintained with a level sensor or sensors 36, which may beconnected to a controller (not shown), to adjust opening of valves andspeed of pumps.

The boron selective resin in the resin beds contains methylglucamine insalt form, such as sulfate or chloride salt form. The resin is oftenmacroporous polystyrene resin.

Boron may be present in a feed water stream in the form of calciumborate (CaB₄O₇). In order to remove boron from the feed water,potassium, ammonium or sodium in hydroxide, carbonate or bicarbonateform is reacted with the feed water. In a preferred embodiment,potassium carbonate (K₃CO₃) or ammonium carbonate ((NH₄)₂CO₃) isdelivered to and reacted with a feed stream, such as with a potassiumpump 40. A stream having calcium carbonate (CaCO₃) and potassium boratesalt (K₂B₄O₇) or ammonium borate salt ((NH₄)₂B₄O₇) is thereby formed.

In an optional initial step, potassium, ammonium, or sodium carbonate issupplied by passing a portion of feed water through a water softenerresin.

The stream having calcium carbonate and potassium borate salt orammonium borate salt is introduced to the open top ambient pressure ionexchange vessel 12 and to the resin containing methylglucamine in saltform. Additionally, potassium carbonate or sodium carbonate is added.The borate is formed on the resin and potassium sulfate or sodiumsulfate is also formed in the water stream.

The present invention permits higher flow rates per square foot of resinand requires less resin bed depth than heretofore known.

Periodically, the system is switched from a service mode to aregeneration mode so that the boron selective resin in the bed of theion exchange vessel 12 is periodically regenerated.

In order to regenerate the resin, a level of liquid in the ion exchangevessel 12 is maintained at a water line level 52. The resin bed isdrained until the liquid level is just above a fluff level, whichoperates in conjunction with a screen 44. This serves to minimize theamount of liquid involved in regeneration. A fluff pump valve 46 isactivated and the outgoing irrigation pump valve 48 is closed. The fluffpump 42 and an acid pump 50 are turned on.

Liquid is passed through the manifold upward in the ion exchange vessel12 which releases carbon dioxide (CO₂) bubbles from the resin that aregenerated by addition of the acid. The bed is also fluidized. This iscontinued until nearly all of the carbon dioxide is released and pH ofless than 7 is maintained. In a preferred configuration, the pH isapproximately 2.1 to 2.5. Removing the carbon dioxide (CO₂) bubblesprevents the regeneration from being compromised. Concentrated sulfuricacid (such as 93%) may be used to minimize volume gain. The overall acidconcentration will be less than 1%.

Thereafter, the outgoing pump 38 is turned on to lower the liquid levelto the top of the resin in the ion exchange vessel 12. The output isdirected to a boron tank 54 past boron tank valve 56. Thereafter, arecycle pump 60 and acid pump 62 deliver water from a recycle tank 64through a spray nozzle or spray bar above the level of the resin. Theacid concentration will be approximately 1% acid. In one example, sprayis turned on for a combined flow of about 1 bed volume per 4 hours withan acid concentration of about 1% acid for 30 minutes. This uniformlydelivers and applies the liquid to the top of the resin bed. The regenpump 38 is controlled to maintain liquid level just above the resin bedwith the level sensors. Thereafter, the acid pump 62 is turned off whilerecycle pump 60 and regen pump remain on. The boron tank valve 56 isopen so that fluid is added to the boron tank.

Thereafter, the recycle pump 60 is turned off, the boron tank valve 56is closed and a recycle tank fill valve 70 is opened. A fresh water pump72 is turned on. The regen out pump 38 also remains on. In one example,this continues for about 2 beds of liquid volume. The recycle tank 74 isfilled from the top without general mixing to maintain boronconcentration gradient. It is preferred that the fresh water has minimalcarbonates in order to minimize CO2 bubble formation. Much of thecarbonate can be released by reducing the pH level of the water to 7 orless.

If the only water available is the well water itself, optionallyfiltering the water with a nanomembrane can remove most of the hardnessto prevent scaling in the evaporator (to be described) and minimize theamount of carbonates present.

FIG. 5 illustrates a sectional view of an evaporator 80 used as a partof the invention.

While efficient regeneration of the resin yields a small volume ofliquid overall, it still represents a large volume of liquid for anirrigation water treatment system. An inexpensive and simple method ofevaporating water is desirable.

The boron tank 54 is in fluid communication with an evaporation pump 82.Fluid in the boron tank 54 is drawn from an upper portion of the tank54. The liquid is pumped and deposited through a nozzle or nozzles abovepacking fill 86 which is spaced above the boron tank. The liquidprogresses downward by gravity. At the same time, ambient air is drawnupward through the packing fill 86 by a fan 88 as shown by arrow 90.

As liquid progresses downward, evaporation occurs and it becomes moreconcentrated. The liquid drops fall to the top of the boron tank asdroplets. The more concentrated, super saturated colder solution isdenser and naturally sinks toward the bottom of the boron tank 54. Ascrystals form, they are even denser, so they naturally sink andaccumulate at the bottom of the boron tank 54, while the less saturatedsolution floats toward the top of the tank 54. The process only requiresa fan 88 and an evaporator pump 82 so it is more energy efficient thanknown evaporators.

In a preferred embodiment, the invention uses ambient air as the soleheat source. The evaporating liquid temperature is less than ambient airtemperature. The invention does not require pressurized or vacuumchambers, chambers, heat exchangers, membranes, compressors, or vacuumpumps. No heat source other than the ambient air is applied to theliquid. The low temperatures and absence of heat exchangers minimizesthe chance of fouling. The only energy required is a fan to move the airpast liquid in an upward direction while a pump moves the liquid to thetop of the packing which progress down as a falling film. In spite ofits simplicity, the energy efficiency is similar or higher than complexevaporators.

In an alternate process, a waste heat source, such as diesel exhaust oran air cooled radiator, provides a thermal energy source.

Whereas, the invention has been described in relation to the drawingsattached hereto, it should be understood that other and furthermodifications, apart from those shown or suggested herein, may be madewithin the scope of this invention.

What is claimed is:
 1. A process for boron removal from feed water,which process comprises: initially reacting potassium, ammonium orsodium in hydroxide, carbonate, or bicarbonate form with calcium borateto form a stream of feed water having a borate salt; introducing saidstream of feed water having borate salt therein through a diffuserscreen to an ion exchange vessel containing macroporous polystyreneboron selective resin in salt form having methylglucamine, said vesselconfigured as a substantially closed container with an open top havingambient pressure and ambient temperature; and periodically regeneratingsaid macroporous polystyrene boron selective resin in said ion exchangevessel by pumping acid into said ion exchange vessel to percolatethrough said resin.
 2. A process as set forth in claim 1 wherein saidstream of feed water is from a subterranean well water or surface watersource.
 3. The process as set forth in claim 1 including drawing saidstream of feed water having borate salt through said macroporouspolystyrene selective resin in said ion exchange vessel.
 4. The processas set forth in claim 3 wherein said stream of feed water is drawnthrough said resin by a pump in fluid communication with manifolds insaid ion exchange vessel.